This invention relates to hydrant valves for the filling of aircraft fuel tanks and the like and more particularly to a safety device for the servo controlled type of hydrant valve wherein a pilot operation of main valve activity is provided. In devices of this type it is usual to have the hydrant valve in the form of a main body portion and a replaceable adaptor secured thereon with appropriate valving mechanisms contained within the housing thus formed. The valving controls the flow of fuel into the hydrant and from the hydrant into the hose coupling and hose leading to the aircraft. The hydrant valve is typically situated in an underground environment and is subject to contamination even though dust caps and covers are provided. Further, the adaptor cap is subject to great abuse in being coupled to very heavy hose coupling devices. Therefore, it is common to need replacement of the adaptor or to gain access to the interior of the hydrant valve for cleaning of contaminants therein or for replacement of valve structures and the like. It is mandatory when removing the adaptor that flow of fuel within the hydrant valve be terminated and this can be accommodated by a manual shut-off valve, a normally-closed pressure responsive servo valve or the like. However, since it is possible to forget to close shut-off valves or to release the override for the automatic servo valve, which is commonly provided by means of a latching detent mechanism, it is desirable to assure that such valve closure has occurred or that such detent mechanism has been disengaged prior to removal of the adaptor housing.
One of the devices disclosed for effecting an interlock between main valve closure and removal of an adaptor structure is shown in the W. F. Hoelzer U.S. Pat. No. 2,693,816. Here it is taught that an interference mechanism of the spokes on a hand wheel which overlie the actuating spindle for the main fuel valve will require closure of the latter and removal of an actuating wrench before the hand wheel can be turned to loosen the adaptor.
Other hydrant couplers having devices therein for controlling the pressure or flow of fuel therein are shown in the Griswold U.S. Pat. No. 3,034,544 and Miller U.S. Pat. No. 3,971,405, the former including an interlock mechanism.